U.S. patent number 5,141,789 [Application Number 07/546,684] was granted by the patent office on 1992-08-25 for self-adhesive sheet.
This patent grant is currently assigned to Kanzaki Paper Manufacturing Co., Ltd.. Invention is credited to Shigeji Matsuzawa, Hideaki Suzuki, Shuichiro Takeda.
United States Patent |
5,141,789 |
Matsuzawa , et al. |
August 25, 1992 |
Self-adhesive sheet
Abstract
Provided herein is an improved self-adhesive sheet composed of a
base member having a water-soluble polymer layer on its reverse
side and a release member, with a pressure sensitive adhesive layer
interposed between them, in which the bond strength between the
water-soluble polymer layer and the pressure sensitive adhesive
layer remains high. It can be stuck readily without moistening; and
yet it can be peeled off easily simply by dipping in water.
Inventors: |
Matsuzawa; Shigeji (Itami,
JP), Suzuki; Hideaki (Kitakatsuragi, JP),
Takeda; Shuichiro (Kobe, JP) |
Assignee: |
Kanzaki Paper Manufacturing Co.,
Ltd. (Tokyo, JP)
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Family
ID: |
27457339 |
Appl.
No.: |
07/546,684 |
Filed: |
June 29, 1990 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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284115 |
Dec 14, 1988 |
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Foreign Application Priority Data
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Dec 16, 1987 [JP] |
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62-319297 |
Jan 30, 1988 [JP] |
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63-20219 |
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Current U.S.
Class: |
428/41.2;
428/342; 428/354; 283/101; 283/71; 283/81; 428/219; 428/350;
428/355CP; 428/355EN; 428/355AC |
Current CPC
Class: |
C09J
7/20 (20180101); Y10T 428/2891 (20150115); Y10T
428/283 (20150115); Y10T 428/2865 (20150115); Y10T
428/2848 (20150115); Y10T 428/277 (20150115); Y10T
428/1448 (20150115); Y10T 428/2878 (20150115) |
Current International
Class: |
C09J
7/02 (20060101); C09J 007/02 () |
Field of
Search: |
;428/342,343,354,40,356,219,355,350 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Davis; Jenna L.
Attorney, Agent or Firm: Wenderoth, Lind & Ponack
Parent Case Text
This application is a continuation of now abandoned application,
Ser. No. 07/284,115 filed on Dec. 14, 1988, now abandoned.
Claims
What is claimed is:
1. A self-adhesive sheet produced by (a) providing (i) a stamp
member having a water-soluble polymer layer on its reverse side
which layer is prepared by applying a coating composition
comprising water-soluble polymer and at least one pigment in an
amount of 5 to 80 wt % on the basis of the total solids in the
water-soluble polymer layer onto the reverse face on the base
member for stamps, and (ii) a release member having a pressure
sensitive adhesive layer prepared by applying a coating composition
comprising an emulsion-type acrylic pressure sensitive adhesive
whose principal component has a glass transition temperature which
is lower than -35.degree. C. and is composed of monomers containing
0.2 to 4.0 wt % of ethylenic unsaturated carboxylic acid onto the
surface of a release base member; (b) superposing said stamp member
(i) through its water-soluble polymer layer onto the pressure
sensitive adhesive layer of said release member (ii); and (c)
subjecting the thus obtained laminate obtained to aging.
2. A self-adhesive sheet according to claim 1, wherein said stamp
member contains postage stamps.
3. A self-adhesive sheet according to claim 1, wherein said
water-soluble polymer layer has a coating weight of 2 to 20
g/m.sup.2 on dry basis.
4. A self-adhesive sheet according to claim 3, wherein said stamp
member contains postage stamps.
5. A self-adhesive sheet according to claim 1, wherein said pigment
contained in said water-soluble polymer layer is a member selected
from the group consisting of calcium carbonate, kaolin and
magnesium carbonate.
6. A self-adhesive sheet according to claim 5, wherein said stamp
member contains postage stamps.
7. A self-adhesive sheet according to claim 5, wherein said
water-soluble polymer layer has a coating weight of 2 to 20
g/m.sup.2 on dry basis.
8. A self-adhesive sheet according to claim 7, wherein said stamp
member contains postage stamps.
9. A self-adhesive sheet produced by (a) providing (i) a stamp
member having a water-soluble polymer layer on its reverse side
which layer is prepared by applying a coating composition
comprising water-soluble polymer and at least one pigment in an
amount of 5 to 80 wt % on the basis of the total solids in the
water-soluble polymer layer onto the reverse face of the base
member for stamps, and (ii) a release member having a pressure
sensitive adhesive layer prepared by applying a coating composition
comprising an emulsion-type acrylic pressure sensitive adhesive
whose principal component has a glass transition which is lower
than -35.degree. C. and produced by copolymerizing 0.2 to 4.0 wt %
of ethylenic unsaturated carboxylic acid monomer, 55 to 95 wt % of
vinyl monomer having an alkyl group with a carbon number of 4 or
more, 4.8 to 44.8 wt % of vinyl monomer having an alkyl group with
a carbon number of below 3, and 0 to 20 wt % of other monomers onto
the surface of a release base member; (b) superposing said stamp
member (i) through its water-soluble polymer layer onto the
pressure sensitive adhesive layer of said release member (ii); and
(c) subjecting the thus obtained laminate obtained to aging.
10. A self-adhesive sheet according to claim 9, wherein said stamp
member contains postage stamps.
11. A self-adhesive sheet according to claim 9, wherein said
water-soluble polymer layer has a coating weight of 2 to 20
g/m.sup.2 on dry basis.
12. A self-adhesive sheet according to claim 11, wherein said stamp
member contains postage stamps.
13. A self-adhesive sheet according to claim 9, wherein said
pigment contained in said water-soluble polymer layer is a member
selected from the group consisting of calcium carbonate, kaolin and
magnesium carbonate.
14. A self-adhesive sheet according to claim 13, wherein said stamp
member contains postage stamps.
15. A self-adhesive sheet according to claim 13, wherein said
water-soluble polymer layer has a coating weight of 2 to 20
g/m.sup.2 on dry basis.
16. A self-adhesive sheet according to claim 15, wherein said stamp
member contains postage stamp.
Description
FIELD OF THE INVENTION
The present invention relates to a self-adhesive sheet which can be
stuck without being moistened and yet can be removed readily
without being deformed by moistening when necessary.
BACKGROUND OF THE INVENTION
Conventional postage stamps and revenue stamps (hereinafter
referred to as "stamps" collectively) have on their reverse side an
adhesive layer formed by coating a water-soluble polymer such as
polyvinyl alcohol. The adhesive layer permits used stamps to be
easily peeled off from envelopes, postcards, etc. by stamp
collectors when dipped in water. However, this advantage is offset
by a disadvantage that the adhesive layer has to be moistened when
stamps are stuck to envelopes and postcards. Moistening needs
water, but water is not always available, and water is often
substituted by saliva. Licking stamps is unsanitary and indecent.
In addition, moistening many stamps is a time-consuming work and
incomplete moistening results in poor adhesion.
In order to eliminate the above-mentioned disadvantage, there was
proposed a stamp of the self-adhesive paper type which can be stuck
simply and efficiently. (See Japanese Utility Model Laid-open Nos.
77700/1977 and 108167/1981.) This stamp has a structure as shown in
FIG. 1 and it comprises a release member 1, a pressure sensitive
adhesive layer 2, a water-soluble polymer layer 3, and a stamp
member 4. When the release member is removed, the stamp member is
ready to be stuck. In actual practice, however, the stamp member of
this structure was found to have a disadvantage that the stuck
stamp member easily peels off even though it is not dipped in
water, because there is not sufficient bond strength between the
pressure sensitive adhesive layer 2 and the water-soluble polymer
layer 3. Therefore, the stamp of this structure is not of practical
use, unless this problem is solved.
On the other hand, conventional self-adhesive labels, seals,
stickers, slips, etc., which do not have any water-soluble polymer
layer as in the case shown in FIG. 1, can be stuck without the need
of being moistened, and they do not peel off easily once they are
stuck. Their disadvantage is that they cannot be easily peeled off
by dipping in water when stamp collectors want to peel them
off.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved
self-adhesive sheet composed of a base member having a
water-soluble polymer layer on its reverse side and a release
member, with a pressure sensitive adhesive layer interposed between
them, in which the adhesive strength between the water-soluble
polymer layer and the pressure sensitive adhesive layer is high
enough to keep the self-adhesive sheet stuck unless it is dipped in
water.
Another object of the present invention is to provide an improved
self-adhesive sheet of the above-mentioned structure which can be
stuck readily in any environment.
To achieve the above-mentioned objects, the present inventors have
carried out a series of researches and as a result, developed an
improved self-adhesive sheet specified herein. The gist of the
present invention resides in a self-adhesive sheet comprising a
base member having a water-soluble polymer layer on its reverse
side and a release member, with a pressure sensitive adhesive layer
interposed between them, characterized in that said water-soluble
polymer layer contains a selected pigment.
The self-adhesive sheet according to the present invention has a
pressure sensitive adhesive layer which is formed from an acrylic
emulsion whose principal component has a glass transition
temperature which is lower than -35.degree. C. and is composed of
monomers containing 0.2 to 4.0 wt % of ethylenic unsaturated
carboxylic acid.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a schematic sectional view showing a conventional
self-adhesive sheet for stamps.
In the figure, there are shown a release member 1, a pressure
sensitive adhesive layer 2, a water-soluble polymer layer 3, and a
stamp member 4.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides a self-adhesive sheet comprising a
base member having a water-soluble polymer layer on its reverse
side and a release member, with a pressure sensitive adhesive layer
interposed between them, characterized in that said water-soluble
polymer layer contains a selected pigment.
The water-soluble polymer that can be used in the present invention
includes, for example, dextrin, starch, oxidized starch,
carboxymethyl starch, dialdehyde starch, polyvinyl alcohol,
polyvinyl methyl ether, polyvinyl pyrrolidone, casein, gum arabic,
tragacanth gum, carboxymethyl cellulose, methyl cellulose, ethyl
cellulose, hydroxyethyl cellulose, polyethylene oxide, sodium
polyacrylate, and water-soluble acrylic resin. They may be used
alone or in combination with one another.
According to the present invention, the water-soluble polymer layer
is incorporated with a pigment. Examples of the pigment include
kaolin, clay, talc, satin white, and lithopone, which are oxides,
hydroxides, carbonates, sulfates, or silicates of magnesium,
aluminum, calcium, barium, zinc, titanium, or silicon such as
magnesium hydroxide, magnesium carbonate, magnesium sulfate,
magnesium silicate, aluminum oxide, aluminum hydroxide, calcium
oxide, calcium hydroxide, calcium carbonate, calcium sulfate,
calcium silicate, barium oxide, barium carbonate, barium sulfate,
zinc oxide, zinc carbonate, zinc sulfate, titanium oxide, and
silicon oxide. They may be used alone or in combination with one
another.
The amount of the pigment to be incorporated into the water-soluble
polymer layer is preferably 3 to 95 wt %, more preferably 5 to 80
wt %, and most preferably 10 to 50 wt %, on the basis of the total
solids in the water-soluble polymer layer. With an amount less than
3 wt %, the pigment does not provide sufficient adhesive strength
between the water-soluble polymer layer and the pressure sensitive
adhesive layer. With an amount in excess of 95 wt %, the pigment
makes the self-adhesive sheet difficult to peel off by dipping in
water.
The water-soluble polymer layer may also be incorporated with, in
addition to the pigment, other adjuvants in an amount not harmful
to the pigment and other components. Examples of the adjuvants
include latices of styrene-butadiene copolymer, methyl
methacrylate-butadiene copolymer, vinyl chloride polymer,
vinylidene chloride polymer, acrylic polymer, vinyl acetate
polymer, and ethylene-vinyl acetate copolymer.
The pigment-containing water-soluble polymer is applied to the
reverse side of a base member for stamps. Coating may be
accomplished in any manner using an air knife coater, roll coater,
blade coater, or bar coater. The coating weight is preferably in
the range of from 2 to 20 g/m.sup.2 on dry basis. With a coating
weight less than 2 g/m.sup.2, the water-soluble polymer layer does
not permit the stamp to peel off readily when dipped in water. With
a coating weight in excess of 20 g/m.sup.2, the water-soluble
polymer layer does not produce any additional effect.
In the meantime, no elucidation has been made yet as to the reason
why the adhesive strength rapidly increases between the
water-soluble polymer layer and the pressure sensitive adhesive
layer when the former is incorporated with a pigment. It is
presumed that the pigment improves anchorage between the two
layers. It is also presumed that the pigment provides metal ions
which contribute to the electrical bond. The pigment provides an
additional effect of preventing blocking when the base member is
wound after the coating of a water-soluble polymer, especially
dextrin.
After the coating of a water-soluble polymer layer, the base member
for stamps is bonded to a release member, with a pressure sensitive
adhesive layer interposed between them. This bonding is usually
accomplished by placing the base member, which has been coated with
a water-soluble polymer layer containing a pigment, on a release
member which has been coated with a pressure sensitive adhesive,
with the water-soluble polymer layer and the pressure sensitive
adhesive layer facing each other. Alternatively, it is also
possible to apply a pressure sensitive adhesive onto the
water-soluble polymer layer and then place a release member on the
pressure sensitive adhesive layer. The former method is preferable
from the viewpoints of drying, curling, and moisture control.
The pressure sensitive adhesive that can be used may be selected
from commonly used ones. Examples are acrylic pressure sensitive
adhesives of emulsion type, solvent type, hot-melt type, and
radiation-curable type; rubber pressure sensitive adhesives of
emulsion type, solvent type, hot-melt type, and radiation-curable
type; and other solvent-type pressure sensitive adhesives based on
silicone, urethane, or vinyl ether.
The object of the present invention is achieved by incorporating a
pigment into the water-soluble polymer layer on the reverse side of
base paper for stamp, as mentioned above. This is not enough for
stamps to stick stable in any environment. Some pressure sensitive
adhesives are easily affected by heat, moisture, and light, and
they still leave room for improvement.
For example, a solvent-type acrylic pressure sensitive adhesive
(which usually contains a large amount of polar groups such as
carboxyl group and hydroxyl group) decreases in adhesive strength
when exposed to an environment of high humidity, because the
carboxyl group or hydroxyl group react with the pigment contained
in the base member for stamps or the water-soluble polymer layer.
An isocyanate-curable solvent-type acrylic pressure sensitive
adhesive becomes yellowed by light, leading to the degradation of
stamps. A rubber-based pressure sensitive adhesive is vulnerable to
degradation by light and liable to migrate to the base member for
stamps when exposed to heat or after storage for a long time. In
addition, a rubber-based pressure sensitive adhesive often causes
trouble when the finished sheet is die-cut into smaller sheets by
stamping.
To eliminate these disadvantages, the present inventors have
carried out a series of researches on a pressure sensitive adhesive
which permits stamps to stick stable in any environment. As a
result, it has been found that the object of the present invention
is achieved in the case where the pressure sensitive adhesive layer
is formed from an acrylic emulsion whose principal component has a
glass transition temperature which is lower than -35.degree. C. and
is composed of monomers containing 0.2 to 4.0 wt % of ethylenic
unsaturated carboxylic acid. This pressure sensitive adhesive
slightly changes in physical properties even after storage for a
long period of time at a high temperature under a high humidity. In
addition, it exhibits a high adhesive strength even when used at
low temperatures and does not cause problems of yellowing by light
and migration of the pressure sensitive adhesive to the substrate.
Moreover, the pressure sensitive adhesive as specified above
permits the finished sheet to be die-cut easily into small pieces
and is suitable for stamps to be used in varied environments.
According to the present invention, the emulsion-type acrylic
pressure sensitive adhesive is limited to one whose principal
component has a glass transition temperature which is lower than
-35.degree. C., so that the pressure sensitive adhesive retains a
sufficient adhesive strength even at low temperatures, say lower
than 0.degree. C. For the pressure sensitive adhesive to retain its
adhesive strength even at a very low temperature, say lower than
-5.degree. C., the glass transition temperature is preferably lower
than -45.degree. C. According to the present invention, the
emulsion-type acrylic pressure sensitive adhesive is limited to the
one whose principal component is composed of monomers containing
0.2 to 4.0 wt % of ethylenic unsaturated carboxylic acid. If the
content of ethylenic unsaturated carboxylic acid is higher than 4.0
wt %, the carboxyl groups or hydroxyl groups in the pressure
sensitive adhesive react with the pigment contained in the
substrate or the water-soluble polymer layer, decreasing the
adhesive strength in an environment of high humidity. Therefore,
the content of ethylenic unsaturated carboxylic acid is preferably
less than 4 wt % or most preferably, less than 2.0 wt %. With a
content less than 0.2 wt %, the pressure sensitive adhesive does
not produce a sufficient adhesive strength and the emulsion has a
poor stability.
Examples of the unsaturated ethylenic carboxylic acid monomer
include acrylic acid, methacrylic acid, itaconic acid, maleic acid,
fumaric acid, 2-methacryloyloxysuccinic acid,
2-methacryloyloxyethylmaleic acid, 2-methacryloyloxyethylphthalic
acid, and 2-methacryloyloxyethylhexahydrophthalic acid.
The above-mentioned ethylenic unsaturated carboxylic acid is
copolymerized with the following monomer to form the emulsion-type
acrylic pressure sensitive adhesive: vinyl monomer having an alkyl
group such as methyl (meth)acrylate, ethyl (meth)acrylate,
isopropyl (meth)-acrylate, lauryl (meth)acrylate, stearyl
(meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate,
cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, isoamyl
(meth)acrylate, isooctyl (meth)acrylate, n-octyl (meth)-acrylate,
dodecyl (meth)acrylate, and isobutyl (meth)-acrylate: vinyl monomer
having a hydroxyl group such as 2-hydroxyethyl (meth)acrylate,
2-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and
3-chloro-2-hydroxy (meth)acrylate: vinyl monomer having an epoxy
group such as diglycidyl (meth)acrylate and methylglycidyl
(meth)acrylate: vinyl monomer having an alkoxy group such as
methoxyethyl (meth)acrylate, ethoxyethyl (meth)acrylate,
butoxyethyl (meth)acrylate, and phenoxyethyl (meth)acrylate: vinyl
monomer having an ethylene oxide group such as diethylene glycol
(meth)acrylate, methoxydiethylene glycol (meth)acrylate,
methoxypolyethylene glycol (meth)acrylate, phenoxydiethylene glycol
(meth)acrylate, and phenoxypolyethylene glycol (meth)acrylate:
vinyl monomer having an amino group such as dimethylaminoethyl
(meth)acrylate, diethylaminoethyl (meth)-acrylate,
N-tert-butylaminoethyl (meth)acrylate, and
methacryloyloxyethyltrimethyl ammonium chloride (meth)acrylate:
vinyl monomer having an amide group such as (meth)acrylamide,
N-methylol (meth)acrylamide, N-methoxymethyl (meth)acrylamide,
N-butoxymethyl (meth)acrylamide, and
N,N'-methylenebis(meth)acrylamide: vinyl monomer having halogen
atoms such as trifluoroethyl (meth)acrylate, pentadecafluorooctyl
(meth)acrylate, 2-chloroethyl (meth)acrylate, 2,3-dibromopropyl
(meth)acrylate, and tribromophenyl (meth)acrylate: vinyl monomer
having a phosphate group such as 2-methacryloyloxyethyldiphenyl
phosphate (meth)acrylate, trimethacryloyloxyethylphosphate, and
triacryloyloxymethy phosphate: vinyl monomer having a sulfonate
group such as sodium sulfopropyl (meth)acrylate, sodium
2-sulfoethyl (meth)-acrylate, sodium vinylsulfonate, sodium
styrenesulfonate, sodium 2-acrylamide-2-methylpropanesulfonate, and
sodium 3-allyloxy-2-hydroxypropanesulfonate: vinyl monomer having a
silane group such as vinyltrimethoxysilane, vinyltriethoxysilane,
vinyltris(.beta.-methoxyethoxy)silane, vinyltriacetoxysilane, and
methacryloyloxypropyltrimethoxy silane: vinyl monomer having a
urethane group such as urethane (meth)acrylate: vinyl monomer
having a phenyl group such as phenyl (meth)acrylate,
p-tert-butylphenyl (meth)acrylate, and o-biphenyl (meth)acrylate:
vinyl monomer having a benzyl group such as benzyl (meth)acrylate:
and vinyl monomer having a tetrahydrofuryl group such as
tetrahydrofuryl (meth)acrylate.
Examples of the copolymerizable monomer include styrene,
chlorostyrene, .alpha.-methylstyrene, vinyltoluene, vinyl chloride,
vinyl acetate, vinyl propionate, veoval 10, acrylonitrile, and
vinyl pyridine
The emulsion-type pressure sensitive adhesive used in the present
invention can be produced by copolymerizing the above-mentioned
monomers. A preferred one is produced by copolymerizing preferably
0.2 to 4.0 wt %. more preferably 0.2 to 2.0 wt % of ethylenic
unsaturated carboxylic acid monomer, 55 to 95 wt % of vinyl monomer
having an alkyl group with a carbon number of 4 or above, 4.8 to
44.8 wt % of vinyl monomer having an alkyl group with a carbon
number below 3, and 0 to 20 wt % of other monomers.
The release member as a component of the self-adhesive sheet of the
present invention is produced by coating or impregnating a
substrate with a release agent such as silicon compound or fluorine
compound. The substrate is glassine paper, clay-coated paper or
craft paper, or wood-free paper coated or laminated with
polyethylene for barrier coating.
The base member for stamps may be a member selected from the group
consisting of wood-free paper, wood pulp paper, art paper, coated
paper, cast-coated paper, metallized paper, synthetic paper, and
film.
The self-adhesive sheet of the above-mentioned structure undergoes
the printing of varied patterns required for stamps. However, it
has printability affected by the water-soluble polymer layer,
pressure sensitive adhesive layer, and release paper. Especially,
in the case of gravure printing commonly used for stamps,
printability depends on the smoothness, ink absorption, and
cushioning of printing sheet. Desirable printability is obtained
when printing sheet is provided with a coating layer composed
mainly of a pigment and an adhesive. A preferred pigment is a
combination of satin white and calcium carbonate having a surface
area of 12,000 to 50,000 cm.sup.2 /g, and a preferred adhesive is a
latex of alkali-sensitive polymer. This coating layer provides a
printing surface having adequate bulkiness, smoothness, and ink
absorption.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention will be described in more detail with reference to
the following examples, which are not intended to restrict the
scope of the invention. In examples, quantities are expressed in
parts by weight, unless otherwise indicated.
EXAMPLE 1
The base paper for stamps was prepared by coating the reverse side
of art paper .sup.(*) with a coating of water-soluble polymer of
the following composition using an air knife coater. The coating
weight was 7 g/m.sup.2 on dry basis.
Polyvinyl alcohol . . . 50 parts
("PVA-105" made by Kuraray Co., Ltd.)
Calcium carbonate . . . 10 parts
("PZ" made by Shiraishi Calcium Co., Ltd.)
Water . . . 540 parts
On the other hand, the layer of pressure sensitive adhesive was
formed by coating commercial polyethylene-laminated release paper
with an emulsion-type acrylic pressure sensitive adhesive.sup.(*)
using a reverse roll coater. The coating weight was 25 g/m.sup.2 on
dry basis.
The base paper coated with a water-soluble polymer and the release
paper coated with a pressure sensitive adhesive were bonded to each
other to form the self-adhesive sheet. The sheet was aged for 20
hours.
Very strong bonding was achieved between the two layers of
water-soluble polymer and pressure sensitive adhesive. When a
specimen, with the release paper removed, was stuck to a stainless
steel plate and peeled off 1 hour later, the two layers did not
separate from each other but the layer of pressure sensitive
adhesive separated from the stainless steel plate.
The thus prepared self-adhesive sheet was found to have good water
removability. When a specimen, with the release paper removed, was
stuck to an envelope and dipped in water for 10 minutes, the base
paper was easily peeled off from the envelope owing to separation
between the two layers of water-soluble polymer and pressure
sensitive adhesive.
EXAMPLE 2
The same procedure as in Example 1 was repeated except that the
base paper for stamps was prepared by coating the reverse side of
cast-coated paper.sup.(*) with a coating of water-soluble polymer
of the following composition using an air knife coater. The coating
weight was 7g/m.sup.2 on dry basis.
Dextrin . . . 50 parts
("Cream dextrin #15" made by Matsutani Kagaku Co., Ltd.)
Kaolin . . . 20 parts
Water . . . 280 parts
The resulting self-adhesive sheet was tested for adhesive strength
between the layers of water-soluble polymer and pressure sensitive
adhesive and also for water-removability in the same manner as in
Example 1. The results are shown in Table 1.
EXAMPLE 3
The same procedure as in Example 1 was repeated except that the
base paper for stamps was prepared by coating the reverse side of
wood-free paper with a coating of water-soluble polymer of the
following composition using an air knife coater. The coating weight
was 7 g/m.sup.2 on dry basis.
Polyvinyl alcohol . . . 50 parts
("PVA-105" made by Kuraray Co., Ltd.)
Oxidized starch . . . 20 parts
("Amicoat #10" made by Matsutani Kagaku Co., Ltd.)
Styrene-butadiene copolymer latex . . . 10 parts
("Nipol L.times.204" made by Nippon Zeon Co., Ltd.)
Magnesium carbonate . . . 20 parts
Water . . . 900 parts
The resulting self-adhesive sheet was tested for adhesive strength
between the layers of water-soluble polymer and pressure sensitive
adhesive and also for water-removability in the same manner as in
Example 1. The results are shown in Table 1.
EXAMPLE 4
The base paper for stamps was prepared by coating the reverse side
of art paper.sup.(*) with a coating of water-soluble polymer of the
following composition using an air knife coater. The coating weight
was 7 g/m.sup.2 on dry basis.
Polyvinyl alcohol . . . 95 parts
("PVA 105" made by Kuraray Co., Ltd.)
Calcium carbonate . . . 15 parts
("PZ" made by Shiraishi Calcium Co., Ltd.)
Water . . . 1000 parts
On the other hand, the layer of pressure sensitive adhesive was
formed by coating commercial polyethylene-laminated release paper
with a pressure sensitive adhesive.sup.(*) using a reverse roll
coater. The coating weight was 25 g/m.sup.2 on dry basis.
The base paper coated with a water-soluble polymer and the release
paper coated with a pressure sensitive adhesive were bonded to each
other to form the self-adhesive sheet. The sheet was aged for 7
days.
The resulting self-adhesive sheet was tested for adhesive strength
between the layers of water-soluble polymer and pressure sensitive
adhesive and also for water-removability in the same manner as in
Example 1. The results are shown in Table 1.
EXAMPLE 5
The base paper for stamps was prepared by coating the reverse side
of art paper.sup.(*) with a coating of water-soluble polymer of the
following composition using an air knife coater. The coating weight
was 7 g/m.sup.2 on dry basis.
Polyvinyl alcohol . . . 10 parts
("PVA-105" made by Kuraray Co., Ltd.)
Calcium carbonate . . . 90 parts
("PZ" made by Shiraishi Calcium Co., Ltd.)
Water . . . 500 parts
On the other hand, the layer of pressure sensitive adhesive was
formed by coating commercial polyethylene-laminated release paper
with a rubber pressure sensitive adhesive.sup.(*) using a die
coater. The coating weight was 25 g/m.sup.2 on dry basis.
* "GM-21" made by Asahi Kagaku Gosei Co., Ltd.
The base paper coated with a water-soluble polymer and the release
paper coated with a pressure sensitive adhesive were bonded to each
other to form the self-adhesive sheet. The sheet was aged for 20
hours.
The resulting self-adhesive sheet was tested for adhesive strength
between the layers of water-soluble polymer and pressure sensitive
adhesive and also for water-removability in the same manner as in
Example 1. The results are shown in Table 1.
COMPARATIVE EXAMPLE 1
The same procedure as in Example 1 was repeated except that the
water-soluble polymer was not incorporated with calcium
carbonate.
The resulting self-adhesive sheet was tested for adhesive strength
between the layers of water-soluble polymer and pressure sensitive
adhesive and also for water-removability in the same manner as in
Example 1. The results are shown in Table 1.
COMPARATIVE EXAMPLE 2
The same procedure as in Example 2 was repeated except that the
water-soluble polymer was not incorporated with kaolin.
The resulting self-adhesive sheet was tested for adhesive strength
between the layers of water-soluble polymer and pressure sensitive
adhesive and also for water-removability in the same manner as in
Example 1.
COMPARATIVE EXAMPLE 3
The same procedure as in Example 3 was repeated except that the
water-soluble polymer was not incorporated with magnesium
carbonate.
The resulting self-adhesive sheet was tested for adhesive strength
between the layers of water-soluble polymer and pressure sensitive
adhesive and also for water-removability in the same manner as in
Example 1. The results are shown in Table 1.
COMPARATIVE EXAMPLE 4
The same procedure as in Example 1 was repeated except that the
base paper for stamps was prepared by coating the reverse side of
wood-free paper with a coating of the following composition using
an air knife coater. The coating weight was 7 g/m.sup.2 on dry
basis.
Styrene-butadiene copolymer latex . . . 80 parts
("Nipol Lx204" made by Nippon Zeon Co., Ltd.)
Magnesium carbonate . . . 10 parts
Water . . . 10 parts
The resulting self-adhesive sheet was tested for adhesive strength
between the layers of water-soluble polymer and pressure sensitive
adhesive and also for water-removability in the same manner as in
Example 1. The results are shown in Table 1.
COMPARATIVE EXAMPLE 5
The same procedure as in Example 1 was repeated except that the
coating of the following composition was used.
Polyvinyl alcohol . . . 98 parts
("PVA-105" made by Kuraray Co., Ltd.)
Calcium carbonate . . . 2 parts
("PZ" made by Shiraishi Calcium Co., Ltd.)
Water . . . 1000 parts
The resulting self-adhesive sheet was tested for adhesive strength
between the layers of water-soluble polymer and pressure sensitive
adhesive and also for water-removability in the same manner as in
Example 1. The results are shown in Table 1.
COMPARATIVE EXAMPLE 6
The same procedure as in Example 1 was repeated except that the
coating of the following composition was used.
Polyvinyl alcohol . . . 4 parts
("PVA-105" made by Kruary Co., Ltd.)
Calcium carbonate . . . 96 parts
("PZ" made by Shiraishi Calcium Co., Ltd.)
Water . . . 300 parts
The resulting self-adhesive sheet was tested for adhesive strength
between the layers of water-soluble polymer and pressure sensitive
adhesive and also for water-removability in the same manner as in
Example 1. The results are shown in Table 1.
EXAMPLE 6
The base paper for stamps was prepared by coating the reverse side
of art paper.sup.(*) with a water suspension of the following
composition using an air knife coater. The coating weight was 7
g/m.sup.2 on dry basis.
Polyvinyl alcohol . . . 5 parts
("PVA-105" made by Kuraray Co., Ltd.)
Kaolin . . . 2 parts
On the other hand, the layer of pressure sensitive adhesive was
formed by coating commercial polyethylene-laminated release paper
with an emulsion-type acrylic pressure sensitive adhesive (having a
glass transition temperature of -48.degree. C.) formed by emulsion
copolymerization of the following components. The coating weight
was 25 g/m.sup.2 on dry basis.
2-ethylhexyl acrylate . . . 80 parts
Vinyl acetate . . . 3 parts
methyl methacrylate . . . 16 parts
acrylic acid . . . 1 part
polyoxyethylene nonylphenol ether (surfactant) . . . 1 part
sodium dioctylsulfosuccinate (surfactant) . . . 1 part
The base paper coated with a water-soluble polymer and the release
paper coated with a pressure sensitive adhesive were bonded to each
other to form the self-adhesive sheet.
The resulting self-adhesive sheet was tested for sticking property
at low temperatures, light resistance, heat resistance, moisture
resistance, and die-cut property. The results are shown in Table
2.
EXAMPLE 7
The same procedure as in Example 6 was repeated except that the
emulsion-type acrylic pressure sensitive adhesive was replaced by
the one (having a glass transition temperature of -37.degree. C.)
formed by emulsion copolymerization of the following
components.
2-ethylhexyl acrylate . . . 68 parts
vinyl acetate . . . 11 parts
methyl methacrylate . . . 18 parts
acrylic acid . . . 3 parts
polyoxyethylene nonylphenol ether (surfactant) . . . 1 part
sodium dioctylsulfosuccinate (surfactant) . . . 1 part
The resulting self-adhesive sheet was tested for sticking property
at low temperatures, light resistance, heat resistance, moisture
resistance, and die-cut property. The results are shown in Table
2.
COMPARATIVE EXAMPLE 7
The same procedure as in Example 6 was repeated except that the
emulsion-type acrylic pressure sensitive adhesive was replaced by
the one (having a glass transition temperature of -31.degree. C.)
formed by emulsion copolymerization of the following
components.
2-ethylhexyl acrylate . . . 63 parts
vinyl acetate . . . 12 parts
methyl methacrylate . . . 20 parts
acrylic acid . . . 5 parts
polyoxyethylene nonylphenol ether (surfactant) . . . 1 part
sodium dioctylsulfosuccinate (surfactant) . . . 1 part
The resulting self-adhesive sheet was tested for sticking property
at low temperatures, light resistance, heat resistance, moisture
resistance, and die-cut property. It was so poor in sticking
property at low temperatures and moisture resistance that it was
not suitable for use as stamps. The results are shown in Table
2.
COMPARATIVE EXAMPLE 8
The same procedure as in Example 6 was repeated except that the
emulsion-type acrylic pressure sensitive adhesive was replaced by
the one (having a glass transition temperature of -48.degree. C.)
formed by emulsion copolymerization of the following
components.
2-ethylhexyl acrylate . . . 80 parts
vinyl acetate . . . 11 parts
methyl methacrylate . . . 3 parts
acrylic acid . . . 6 parts
polyoxyethylene nonylphenol ether (surfactant) . . . 1 part
sodium dioctylsulfosuccinate (surfactant) . . . 1 part
The resulting self-adhesive sheet was tested for sticking property
at low temperatures, light resistance, heat resistance, moisture
resistance, and die-cut property. It was so poor in moisture
resistance that it was not suitable for use as stamps. The results
are shown in Table 2.
COMPARATIVE EXAMPLE 9
The same procedure as in Example 6 was repeated except that the
emulsion-type acrylic pressure sensitive adhesive was replaced by
the one (having a glass transition temperature of -31.degree. C.)
formed by emulsion copolymerization of the following
components.
2-ethylhexyl acrylate . . . 63 parts
vinyl acetate . . . 12 parts
methyl methacrylate . . . 23 parts
acrylic acid . . . 2 parts
polyoxyethylene nonylphenol ether (surfactant) . . . 1 part
sodium dioctylsulfosuccinate (surfactant) . . . 1 part
The resulting self-adhesive sheet was tested for sticking property
at low temperatures, light resistance, heat resistance, moisture
resistance, and die-cut property. It was so poor in sticking
property at low temperatures that it was not suitable for use as
stamps. The results are shown in Table 2.
COMPARATIVE EXAMPLE 10
An attempt was made to prepare an emulsion-type acrylic pressure
sensitive adhesive by emulsion copolymerization of the following
components; but it was impossible to perform polymerization on
account of coagulation which occurred in the initial stage of
polymerization.
2-ethylhexyl acrylate . . . 80 parts
vinyl acetate . . . 3 parts
methyl methacrylate . . . 16.9 parts
acrylic acid . . . 0.1 parts
polyoxyethylene nonylphenol ether (surfactant) . . . 1 part
sodium dioctylsulfosuccinate (surfactant) . . . 1 part
COMPARATIVE EXAMPLE 11
The same procedure as in Example 6 was repeated except that the
pressure sensitive adhesive was replaced by a solvent type acrylic
pressure sensitive adhesive ("PE-154" made by Nippon Carbide Co.,
Ltd.).
The resulting self-adhesive sheet was tested for sticking property
at low temperatures, light resistance, heat resistance, moisture
resistance, and die-cut property. It was so poor in moisture
resistance that it was not suitable for use as stamps. The results
are shown in Table 2.
COMPARATIVE EXAMPLE 12
The same procedure as in Example 6 was repeated except that the
pressure sensitive adhesive was replaced by a solvent-type acrylic
pressure sensitive adhesive composed of 100 parts of "AT-D10H"
(made by Saiden Kagaku Co., Ltd.) and 1 part of "Curing Agent A"
(made by Saiden Kagaku Co., Ltd.).
The resulting self-adhesive sheet was tested for sticking property
at low temperatures, light resistance, heat resistance, moisture
resistance, and die-cut property. It was so poor in light
resistance and moisture resistance that it was not suitable for use
as stamps. The results are shown in Table 2.
COMPARATIVE EXAMPLE 13
The same procedure as in Example 6 was repeated except that the
pressure sensitive adhesive was replaced by a rubber-based pressure
sensitive adhesive "GM-21" (made by Asahi Gosei Kagaku Co.,
Ltd.).
The resulting self-adhesive sheet was tested for sticking property
at low temperatures, light resistance, heat resistance, moisture
resistance, and die-cut property. It was so poor in light
resistance, heat resistance, and die-cut property that it was not
suitable for use as stamps. The results are shown in Table 2.
TABLE 1 ______________________________________ Adhesive strength
Water removability ______________________________________ Example 1
Good Good Example 2 Good Good Example 3 Good Good Example 4 Good
Good Example 5 Good Good Comparative Example 1 Poor Good
Comparative Example 2 Poor Good Comparative Example 3 Poor Good
Comparative Example 4 Good Poor Comparative Example 5 Poor Good
Comparative Example 6 Good Poor
______________________________________
TABLE 2
__________________________________________________________________________
Sticking at Light Heat Moisture Die-cut low temperature resistance
resistance resistance property
__________________________________________________________________________
Example 6 Good Good Good Good Good Example 7 Fair Good Good Fair
Good Comparative Example 7 Poor Good Good Poor Good Comparative
Example 8 Good Good Good Poor Good Comparative Example 9 Poor Good
Good Good Good Comparative Example 11 Fair Good Good Poor Good
Comparative Example 12 Good Poor Good Poor Good Comparative Example
13 Fair Poor Poor Fair Poor
__________________________________________________________________________
Note: Sticking at low temperature Sticking property at temperatures
lower than 0.degree. C. Light resistance Resistance of the pressure
sensitive adhesive to yellowing which occurs with time upon
exposure to light. Heat resistance Resistance of the pressure
sensitive adhesive to migration to the base paper stamps which
occurs at high temperatures. Moisture resistance Sticking property
which is retained after standing i a highhumidity environment.
Die-cut property Ability of the selfadhesive sheet to be diecut
into smaller size by stamping.
* * * * *